Structure and Functions of the Soil Food Web: Understanding Healthy Soils

1. Structure and Functions of theSoil Food Web:Understanding Healthy Soils The organisms involved How they interact What they do Monitoring food web condition Food web management Howard Ferris Department of Nematology University of California, Davis hferris@ucdavis.edu November, 2005

2. Heat and CO2 • Carbon is respired and Energy is used by each organism in the web • The amounts of Carbon and Energy available determine the size and activity of the web Resources Soil Food Web Structure – Resource Effects Organic Source

3. Linear Food Chains

4. Linear Food Chains and Trophic Cascades But consider.. Bottom up effects Omnivory

5. A more likely structure… The Trophic Network Or Food Web

6. Functional Guilds

7. Soil Food Web Structure – Biotic Effects

8. Positive and Negative Feedback in Food Web Structure Sinorhizobium meliloti and bacterivore nematodes 0 nematodes 5 nematodes With twenty nematodes Fu et al. 2005

9. Soil Food Web Structure – Environmental Effects Environmental heterogeneity Zones and Gradients: texture structure temperature water O2 CO2 NO3 NH4 minerals Separate metacommunities?

10. Food Web Structure - Patchiness • Resource distribution • Spatial heterogeneity • Organism motility • Omnivory • Strong and weak links • Microsite asynchrony • Viewing resolution

11. Functional Complementarity Functional Redundancy Functional Group Diversity Strength of Function or Service Functional Group Diversity Loreau, Oikos 2004 Structure and Function: Abundance and Diversity consumers resource

12. Soil Food Webs - Function • Decomposition of organic matter • Cycling of minerals and nutrients • Reservoirs of minerals and nutrients • Redistribution of minerals and nutrients • Sequestration of carbon • Degradation of pollutants, pesticides • Modification of soil structure • Community self-regulation • Biological regulation of pest species

13. Soil Food Web Structure and Function - the need for indicators

14. The Nematode Fauna as a Soil Food Web Indicator Herbivores Bacterivores Fungivores Omnivores Predators

15. Why nematodes as bioindicators? • Occupy key positions in soil food webs • Standard extraction procedures • Identification based on morphology • Clear relationship between structure and function • The most abundant of the metazoa • Each sample has high intrinsic information value

16. Functional Diversity of Nematodes

17. Enrichment Indicators Structure Indicators • Rhabditidae • Panagrolaimidae • etc. • Short lifecycle • Small/ Mod. body size • High fecundity • Small eggs • Dauer stages • Wide amplitude • Opportunists • Disturbed conditions • Aporcelaimidae • Nygolaimidae • etc. • Long lifecycle • Large body size • Low fecundity • Large eggs • Stress intolerant • Narrow amplitude • Undisturbed conditions Basal Fauna • Cephalobidae • Aphelenchidae, etc. • Moderate lifecycle • Small body size • Stress tolerant • Feeding adaptations • Present in all soils

18. Testable Hypotheses of Food Web Structure and Function • Disturbed • N-enriched • Low C:N • Bacterial • Conducive • Maturing • N-enriched • Low C:N • Bacterial • Regulated Enriched Ba1 Enrichment index Structured Fu2 • Degraded • Depleted • High C:N • Fungal • Conducive • Matured • Fertile • Mod. C:N • Bact./Fungal • Suppressive Fu2 Basal Ba2 Om4 Om5 Basal condition Ca3 Ca4 Ca5 Fu3 Fu4 Fu5 Ba3 Ba4 Ba5 Structure index Ferris et al. (2001)

19. 100 Tomato Systems Yolo Co. Prune Orchards Yuba Co. Enrichment Index 50 Redwood Forest and Grass Mendocino Co. Mojave Desert 0 0 50 100 Structure Index Food Web Analyses

20. Management of Food Web Structure: Carbon Pathways and Pools Herbivore Fungal Omnivory Decomposition Bacterial channelized reticulate

21. Carbon Channel Management • Bacterivore Channel • “Fast Channel” • Moisture • Low C:N, labile substrates • High respiration and turnover • Mineralization of nutrients • Major predators are protozoa and nematodes • Herbivore Channel • “Intermediate Channel” • Host status and defense mechanisms • Damage to host • Substrate respiration and immobilization, excretion and defecation • Major predators are fungi and nematodes • Fungivore Channel • “Slow Channel“ • High C:N, lignin, cellulose, resistantsubstrates • Conservation of carbon, greater web structure • Major predators are microarthropods and nematodes

22. P Regulatory function P F O Pr O Pr F B Nutrient function B Structure and Function

23. Inflow Channel Analysis

24. Succession C supplied Resource transformation Community structure shifts Ferris and Matute (2003)

25. Resource transformation • Channel Index: • a weighted ratio of fungivore and bacterivore nematodes • higher CI indicates more fungal Ferris and Matute (2003)

26. what if? Food Web channel management: Nature and timing of carbon sources Data adapted from McSorley and Frederick. 1999.

27. external sources external sources rhizodeposition rhizodeposition old root death old root death C herbivory herbivory Food for the Soil Food Web C

28. Mineralization potential of fungal- and bacterial-feeding nematodes C:N = 8.5:1 C:N = 8.3:1 C:N = 4:1 C:N = 6:1 Soil Food Web Management - Experiment and Observation

29. Sustainable Agriculture Farming Systems Project 1988-2000

30. Cover crop Cover crop Irrigation temperature moisture T0 activity M0 Soil Food Web Management - experiment

32. 100 100 50 50 0 0 0 50 100 0 50 100 How Fragile is the Food Web? Sampled 2000 Organically-managed for 12 years Sampled 2001 After Deep Tillage Enrichmentindex Structure index Structure index Berkelmans et al. (2003)

33. Ammonium sulfate 200 Nematode guild 150 c-p 1 Standardized Counts c-p 2 X 100 c-p 3 c-p 4 50 c-p 5 X X X X X 0 0 0.02 0.05 0.1 0.5 1 Concentration (mM-N) Nematode Sensitivity – Mineral Fertilizers Tenuta and Ferris (2004)

34. Disadvantages: ↓Productivity ↑Continuous ↑Monitoring ↑Rotation ↑Risk ? Equipment ? Economics ? Labor ? Knowledge base Advantages: ↓Tillage ↓Fossil fuel ↓Dust ↓Leaching ↑Soil structure ↑Porosity ↑Food web structure ↓Pesticides ↓Mineral fertilizers ↓Weeds and herbicides ↓Water ↓Costs ↑Sustainability Surface mulch with designed C:N ratio Pest resistance/tolerance Undisturbed bed Buried drip Transplant inoculants: Entomopathogenic nematodes Rhizobia Flourescent pseudomonads Nematode-trapping fungi

35. Some References • Bongers, T., H. Ferris. 1999. Nematode community structure as a bioindicator in environmental monitoring. Trends Ecol. Evol. 14, 224-228. • Ferris, H., T. Bongers, R. G. M. de Goede. 2001. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Appl. Soil Ecol. 18, 13-29. • Ferris, H., M.M. Matute. 2003. Structural and functional succession in the nematode fauna of a soil food web. Appl. Soil Ecol. 23:93-110. • Loreau M. 2004. Does functional redundancy exist? Oikos 104:606-611. • Neher, D. A., T. R. Weicht, D. L. Moorhead, R. L. Sinsabaugh. 2004. Elevated CO2 alters functional attributes of nematode communities in forest soils. Funct. Ecol. 18:584-591. • Tenuta, M., H. Ferris. 2004. Relationship between nematode life-history classification and sensitivity to stressors: ionic and osmotic effects of nitrogenous solutions. J. Nematol. 36:85-94. • Yeates, G. W., R. Cook. 1998. Nematode fauna of three Welsh soils under conventional and organic grassland farm management. Pp. 305-313 in R. de Goede and T. Bongers, eds. Nematode Communities of Northern Temperate Grassland Ecosystems. Giessen, Germany: Focus Verlag. More information: http://plpnemweb.ucdavis.edu/nemaplex